Usually, a tubular material or a bar material is subject to a chamfering work for chamfering a cut surface thereof by a chamfering machine so that it can be used in an industrial field or at home. The chamfering work is necessary not only for securing the safety by removing a sharp cut surface but also for forming a bead surface for welding.
Further, the chamfering machine is also used in a surface cutting work for cutting an outer peripheral surface, as well as the chamfering work.
As shown in FIG. 1, a chamfering machine, which we usually use, includes a chamfering machine body 11 having an electric motor attached thereto, a chamfering cutter 12 which is connected to the electric motor and cuts a workpiece by using a rotational force provided by the electric motor, an adjustment lever 13 installed on an upper part of the chamfering machine body 11 to adjust the elevating height of the chamfering cutter 12, and a guide 20 installed at a part under the chamfering cutter 12 in a state in which the guide is bent by 90 degrees in order to enable a more convenient chamfering work. Further, the guide 20 has a structure which can be rotated about the chamfering cutter 12 for shifting between works, such as chamfering and surface cutting.
Therefore, as shown in FIG. 2, by properly rotating the guide 20 according to the work, it is possible to perform various works, such as chamfering (a) and surface cutting (b) of a flat plate, and chamfering (c) and surface cutting (d) of a tubular material or bar material.
In this event, although the other works make no problem, the surface cutting (d) of a tubular material or bar material requires a high level of technical skill. That is, as shown in FIG. 3, for surface cutting of a tubular material (p), the chamfering cutter 12 first approaches the tubular material (p) from the outside thereof as shown in (a), and the surface of the tubular material (p) starts to be cut as soon as the chamfering cutter 12 comes into contact with the tubular material (p) as shown in (b). Further, as the chamfering cutter 12 enters more deeply as shown in (c), the thickness by which the tubular material (p) is cut increases.
Further, the surface cutting starts when the chamfering cutter 12 enters while cutting out the outer peripheral surface of the circular material (p) as shown in FIG. 4, and the thickness of the surface cutting gradually decreases from the moment when the chamfering cutter 12 goes over the center of the upper surface of the circular material (p). Further, at the point where the central part of the chamfering cutter 12 and the upper surface of the circular material are aligned with each other, the upper surface of the circular material is not in contact with the cutting tip 12a of the chamfering cutter 12 any longer and thus idly rotates without being cut. This is because the chamfering cutter 12 has a cylindrical shape and has the cutting tip 12a attached to the circumferential surface thereof. Therefore, the cutting work is not performed any longer after the cutting surface reaches the central portion of the chamfering cutter.
In a vertical chamfering machine wherein the principal axis of the chamfering cutter and the axial center of the circular material perpendicularly meet each other, as shown in FIG. 4, the thickness of the surface cutting changes according to the portion in contact with the lower end of the chamfering cutter regardless of how constant the height of the chamfering cutter relative to the guide is. Of course, as noted from the third figure, the cutting work may not be achieved at all.
For a more detailed description, referring to FIG. 5 which shows in more detail than FIG. 4, as noted from the lower front view, at the moment when the chamfering cutter comes into contact with one side of the circular material, the outer surface of the circular material is cut out as much as indicated by the thin solid line by the portion in contact with the cutting end of the cutting tip. In other words, as noted from the upper plan view, the surface the circular material in contact with a part of the outer periphery of the chamfering cutter is a cut surface, and the hatched portion lengthily extending on the outer peripheral surface of the circular material from the cut surface is a surface to be cut with a predetermined cutting width.
In this state, if the chamfering cutter proceeds further in the proceeding direction, the cutting width increases and the cutting depth (d) also increases. That is, the cutting depth is determined according to how much the chamfering cutter is pushed into the cut surface by the worker's hand. Therefore, it is impossible to precisely set the cutting depth according to optional selection based on the naked eye and the force applied by the hands.
Moreover, as noted from FIG. 6, in the cutting work when the cutting tip of the chamfering cutter has passed over the central line of the circular material, the portion of the circular material in contact with the cutting tip is cut as noted from the part hatched by the right uphill lines while the central portion of the circular material which is not in contact with the cutting tip is not cut as noted from the part hatched by the right downhill lines. The situation as shown in FIG. 6 corresponds to a situation when the cutting tip and the circular material come into contact with each other for the first time. However, when the circular material has rotated more or the chamfering cutter has progressed more, further cutting is not performed, which may cause a load to a non-cutting section between the circular material and the chamfering cutter or may make the chamfering machine bounce.
In order to solve the problem as described above, as shown in FIG. 7, another technique employs a guide 20b, which extends downward and has moving guide rolls 22 installed thereon, wherein, after selection of the cutting position of the chamfering cutter 12, the guide rolls 22 are fixed to and in tight contact with the outer peripheral surface of the tubular material (p) so that they can be used as an auxiliary means for the chamfering work.
However, although the guide rolls 22 as described above may be an improvement in the working method, they are not enough to deal with an unavoidable defect of the tubular material (p). That is, as noted from FIG. 8, when the tubular material (p) has an ellipsoidal shape, the guide rolls 22 sliding on the tubular material (p) while being in tight contact with both sides thereof may change the cutting position of the chamfering cutter 12 while moving upward or downward according to the curvature of the tubular material.
The tubular material (p) may be not only ellipsoidal but also uneven. In fact, when the tubular material (p) is ellipsoidal or uneven, there are considerably many more defects than expected. However, there is a tendency in the field using the tubular material that the defects in the chamfering work are given short shrift since the defects are thought as a problem of the raw material itself, which is a tubular material.